This invention relates to a high melting silicide target for use as an electrode material or a wiring material in a semi-conductor device, particularly a sputtering target having a fine texture and a high density and a process for preparing the same.
Recently, high melting metal silicides such as silicides of molybdenum, tungsten, titanium, etc. having a low resistivity have been used as electrode materials or wiring materials for LSI and ultra LSI. In order to form films of high melting point metal silicides, sputtering and chemical vapor phase deposition processes have been used. From the viewpoint of film productivity and safety at the film production, the sputtering process is mainly used.
Heretofore, such silicide targets have been prepared by melting or powder sintering. In order to prevent cracking of the targets due to sputtering or prevent formation of projections or asperities on the target surface due to local electric discharge during the sputtering, various processes for preparing targets of high density, thereby reducing the voids in the target, have been proposed.
For example, Japanese Patent Application Kokai (Laid-Open) No. 61-145828 discloses that a high density target can be obtained by mixing high purity, high melting metal powder with high purity silicon powder, molding the resulting mixture under pressure, sintering the molding with heating and melting the sintered product with an electron beam, thereby producing a molten silicide product, where the molten silicide product texture contains crystal grains having grain sizes of 0.2 to 0.5 mm owing to the electron beam melting.
Japanese Patent Application Kokai (Laid-Open) Nos. 61-141673 and 61-141674 disclose that a high density target can be obtained by mixing molybdenum or tungsten powder with silicon powder, followed by molding and silicidizing, and disintegrating the resulting pellets into powder and hot pressing the powder, thereby producing a sintered product.
Japanese Patent Application Kokai (Laid-Open) No. 61-141673 proposes a process for increasing the purity of the target based on the so called wet refining procedure comprising dissolution in nitric acid and successive dissolution in ammonia with heating in order to reduce the contents of alkali metals and radioactive elements.
As described above, various processes have been proposed for preparing high density targets in order to reduce the voids in the targets. The process utilizing electron beam melting has the disadvantages that the molten silicide product texture contains crystal grains having grain sizes of 0.2 to 0.5 mm and thus the target texture cannot be made finer and further that changes on the sputtered surface due to structurally different stoichiometric compositions MSi.sub.2 where M stands for a high melting point metal, such as WSi.sub.2, MoSi.sub.2, TiSi.sub.2, etc. and also due to free Si grains, cannot be thoroughly reduced.
The process utilizing silicidizing, followed by disintegration of pellets into powder and hot pressing of the powder, thereby obtaining a sintered product, has the disadvantages that the oxygen content of the resulting powder is increased during the disintegration of the pellets, so that no better film can be formed.